Field of the Invention
The present invention relates to a robot apparatus including a multi-articulated robot and a method for controlling a multi-articulated robot.
Description of the Related Art
In recent years, robot apparatuses that cause multi-articulated robots to perform work such as assembling of workpieces have been increasingly developed. Such robot apparatuses ultimately aim at moving the multi-articulated robots like human hands and cause the multi-articulated robots to perform work such as assembling of complicated workpieces at high speed.
Unfortunately, a multi-articulated robot has a plurality of postures, so-called singular points, at which one position and posture designated in a three-dimensional space cannot be determined as one in a joint space, and the singular points prevent the multi-articulated robot from being intricately moved at high speed. Hence, it is important to appropriately process such singular points in the robot apparatus development.
A block diagram of a general controlling apparatus that controls a multi-articulated robot is illustrated in FIG. 13. In FIG. 13, a current position Ci denotes a position and a posture of a hand tip of a manipulator represented in a three-dimensional space, and a deviation command Vi denotes a deviation of the position and the posture of the hand tip for each control cycle (for example, 2 ms) decided in advance. Because the control cycle is constant, the deviation command Vi represents the speed, and is generated for each control cycle using a teaching pendant and the like.
In such a configuration, a position command calculating unit 150 adds the deviation command Vi to the current position Ci to obtain a next position Ci+1, and an inverse kinematics calculating unit 155 performs inverse kinematics calculation on the next position Ci+1 to obtain a next joint angle command qi+1. Then, this is transmitted to a servo controlling apparatus 130 that controls joints of the multi-articulated robot, whereby the multi-articulated robot is drive-controlled. However, if the multi-articulated robot is located in the vicinity of a singular point, the joint angle command qi+1 significantly changes from the previous joint angle command qi, and the multi-articulated robot may move quickly.
A method of limiting the joint angle command speed is conceivable to deal with the above-mentioned problem. However, if the joint angle command speed is limited, the multi-articulated robot may significantly deviate from the original target position of the hand tip, and a return to the original target position becomes difficult once the multi-articulated robot deviates therefrom. According to a technique disclosed to deal with this problem, if the joint angle speed is excessive, a speed limitation for deceleration is put, whereby the multi-articulated robot is prevented from quick movement in the vicinity of the singular point (Japanese Patent Application Laid-Open No. 2003-300183).
Unfortunately, in the technique disclosed in Japanese Patent Application Laid-Open No. 2003-300183, the joint angle speed is always limited, and hence a motion of the multi-articulated robot becomes slower at a position and a posture other than the singular point.